Field of the Invention
The present disclosure relates to an organic light emitting display device, and more particularly, to a top emission type organic light emitting display device.
Discussion of the Related Art
An organic light emitting display (OLED) device is an emissive type display device where an electron of a first electrode and a hole of a second electrode are injected into an emission portion and a light is emitted when an exciton generated by the combination of the electron and the hole transitions from an excited state to a ground state.
Since the OLED device has excellent properties such as a wide viewing angle, a fast response speed and a high contrast ratio, the OLED device may be used as a graphic display, a display for television and a surface light source. In addition, the OLED device is suitable for a next generation flat panel display because of its thin profile, light weight and excellent color gamut. Further, the OLED device has an advantage such that the OLED device may be formed by using a flexible transparent substrate such as a plastic substrate.
The OLED device may be classified into a top emission type and a bottom emission type according to an emission direction of a light. The bottom emission type OLED device has a high stability and a high degree of freedom in process. However, since the bottom emission type OLED device has a limitation in aperture ratio, it is difficult to apply the bottom emission type OLED device for a high resolution product. Recently, as a result, the top emission type OLED device has been widely used.
FIG. 1 is plan view showing a stripe type pixel of an organic light emitting display device according to the related art. In FIG. 1, a stripe type pixel P includes red, green and blue sub-pixels SPr, SPg and SPb which are all arranged along a horizontal direction. Each of the red, green and blue sub-pixels SPr, SPg and SPb includes an emission area EA, and the emission areas EA of the red, green and blue sub-pixels SPr, SPg and SPb emit lights having colors different from one another.
In the organic light emitting display (OLED) device having the stripe type pixel, generally, an organic material is deposited on a substrate using a shadow mask having a plurality of open patterns. As a result, an organic emitting layer having a plurality of organic thin film patterns separated from one another is formed on the substrate, and the plurality of organic thin film patterns of the organic emitting layer emit a red-colored light, a green-colored light and a blue-colored light.
Even when the OLED device is a top emission type, the plurality of organic thin film patterns emitting lights having different colors are spaced apart from one another by a gap to prevent a shadowing effect caused by an ambiguous border between adjacent organic thin film patterns. A gap area defined by the distance of the gap is a non-emissive region and may be referred to as a dead zone. The dead zone makes it difficult to obtain a high color reproducibility and a high resolution in the OLED device.
An OLED device may be classified into a passive matrix type organic light emitting display (PMOLED) device and an active matrix type organic light emitting display (AMOLED) device according to a method of driving an organic light emitting diode. The AMOLED device includes a plurality of scan lines, a plurality of data lines, a plurality of power lines and a plurality of pixels. The plurality of pixels are connected to the plurality of scan lines, the plurality of data lines and the plurality of power lines and are arranged in matrix. Generally, each of the plurality of pixels includes a light emitting diode (LED), a driving thin film transistor (TFT) adjusting an amount of current supplied to the LED, a switching TFT transmitting a data signal to the driving TFT and a storage capacitor keeping a voltage of the data signal.
Although the AMOLED device has an advantage in power consumption, the AMOLED device has non-uniformity in display because intensity of the current flowing through the driving TFT changes due to a deviation in threshold voltage defined by the voltage difference between a gate electrode and a source electrode of the driving TFT. Since the property of the TFT in the pixels changes according to process parameters, the driving TFTs in the pixels have a deviation in threshold voltage. To overcome the non-uniformity in the display between the pixels, a compensating circuit that compensates the threshold voltage of the driving TFT is further formed in the pixel. The compensating circuit includes a plurality of driving elements. However, since the compensating circuit including the plurality of driving elements is formed in a limited region of each sub-pixel, degree of freedom in design and integration of the driving elements for the LED is further restricted.